The Arctic dipole and North Siberian oscillation

There is evident asymmetry in Arctic ice retreat (Belchansky et al. 2005). This process is occurred most actively in the Eastern Arctic and rather neutral in Western Arctic. During a second half of last century the SLP anomaly field in high latitudes had monopole structure centered at North Pole. In 1950s and 1960s it was a positive monopole, but in 1980s and 1990s - a negative monopole. Since the beginning of 21st century an appearance of SLP dipole pattern (see also Wu et al. 2005) was observed. This pattern has two pole of opposite signs: one in high latitudes of Eastern Hemisphere, other - in Western Hemisphere. Strongest SLP

dipole anomaly with account to amplitude was observed in October 2003-2006. One can deduce that there is a link between enhancement of air-sea energy exchange in Kara and Laptev Seas, on one hand, and appearance of dipole structure in SLP field in polar area, on other hand. North Atlantic Oscillation (NAO) index is related to the difference between Azores and Iceland SLP. A vast pool of no-freezing waters in high latitudes surrounds Iceland. Now days most part of Kara Sea is free of ice during late summer and early autumn. This fact gave us a hint on possibility of similar effect on atmospheric SLP. Therefore, we decided to investigate a new climate index - North Siberian Oscillation (NSO) as a twin to NAO. It is a normalized difference between Azores and station "Island Dixon" (in Kara Sea) SLP. September curves of NAO (dotted) and NSO (solid) are in a good agreement (Fig. 6). The NSO growth since the beginning of this century is even a more rapid than those of NAO. Latter might be explained by

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Fig. 6. Comparison of the September NAO (dotted line) and NSO (solid line).

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Fig. 6. Comparison of the September NAO (dotted line) and NSO (solid line).

Fig. 7. Comparison of the September AO (dotted line) and NSO (solid line).

abrupt increasing of SST in Kara Sea (see Fig. 4) during last decade. Similar plots were drawn for other autumn and winter months. All of them demonstrated analogical behavior with NAO. It is known that NAO determines intensity of meridian circulation over North Atlantic. Below we will show that NSO plays now a similar role in Asia. NSO comparison with Arctic Oscillation (AO) index, which represents a coefficient with the first EOF in the high latitude SLP field expansion, demonstrates that there were two different periods: its resemblance in 1950-1995 and similarity occurred during last decade (Fig. 7). Both figures (Figs. 6 and 7) give substantial support to above assumption that rapid ice melting leads to fundamental changes in the atmospheric circulation regimes in Northern Asia.

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